Quantum point contact as a local probe of the electrostatic potential contours

Quantum point contacts, shifted laterally by ±50 nm have been used to study the local electrostatic potential in the two-dimensional electron gas of a GaAs-${\mathrm{Al}}_{\mathit{x}}$ ${\mathrm{Ga}}_{1\mathrm{-}\mathit{x}}$As heterostructure. The resistance of the quantized plateaux is observed to vary with this lateral position. In one device an alternate suppression of the quantized resistance plateaux is observed, which we interpret as being due to an overlap of strong local potential fuctuations with the transverse profile of the wave functions in the quantum point contact.